This invention relates to an electrochemical system partly implantable into a body for detecting glucose concentrations therein and in a similar fashion, other elements, compounds or analytes.
There is a need for an implantable generic device that can be used with different types of electrochemical sensors to facilitate real time monitoring during sensor development. Such a device would be an integrated potentiostat telemetry transmitting unit allowing researchers to test various biosensor configurations for multiple possible uses. In an effort to regulate their glucose levels, diabetic patients monitor their glycemia by repeatedly obtaining a sample of capillary blood by finger-pricking. Since these tests are frequent, painful and time consuming, diabetic patients resist performing an adequate number of these daily glucose measurements. This low compliance, plus the intrinsically discontinuous nature of the technique, leads to the extensive pathology seen in diabetic patients. Thus, a great deal of research is being directed toward the development of new glucose sensors capable of replacing finger-pricking. Such glucose sensors are ideally implantable in the patient, though pain free, as well as small, light-weight and capable of reliable and continuous operation over extended periods of time. In addition it is desirable that such sensors be a part of a system capable of continuous and real time processing of data from the sensors for diagnosis and patient treatment. It is also desirable that the system be easily adaptable to use with various amperometric glucose sensors without the need for redesigning the system for each new sensor. Such a system should be flexible, reliable, stable and easy to use in a telemetried system.
Previous telemetried systems require the development of designs taylored to a specific use and set of requirements. Typical telemetried systems utilize voltage-to-frequency conversion to increase frequency stability during frequency modulation of a carrier signal. This method expends objectionable amounts of power, limiting battery lifetime. The transmitted radio frequency carrier and modulation thereof are continuous battery consuming processes. However, this requires the additional step of demodulation and additional signal shaping circuits in order to recover the data. This requires additional power consumption and increased package size. In addition, data accuracy can be tainted by drift in the transmitter and the receiver components. Typical telemetried systems also required dual battery configurations to provide power, thus adding to size.
It is desirable in a telemetried system to convert glucose sensor data to digital values in vivo, in order to avoid conversion and modulation errors. Once in digital format, a radio transmitter can utilize a serial data transmission protocol to a receiver thence directly to a computer for processing. An on-off-keyed(OOK) asynchronous serial binary character data transmission method expends battery power only for the brief duration of each digital xe2x80x9conexe2x80x9d bit. It expends zero power for each digital xe2x80x9czeroxe2x80x9d bit. In addition to the glucose sensor data, an individual sensor identification code, and error preventive codes are included in each transmission, termed a xe2x80x9cpacket.xe2x80x9d These data packets uniquely identify one of any number of sensors and provide a means to verify fidelity of the received data. Stored programs can allow direct conversion to glucose concentrations for immediate readout.
Monitoring glucose concentrations in diabetic patients is seen in U.S. Pat. No. 4,633,878 which relates to feedback controlled or xe2x80x9cclosed-loopxe2x80x9d insulin pumps known also as xe2x80x9cartificial pancreasesxe2x80x9d. These devices provide a continuous glucose determination in the diabetic patient. Data is transmitted from a glucose sensor to a microprocessor unit, which controls a pump for insulin, or glucose, infusion in order to maintain blood glucose levels within physiological range. In U.S. Pat. No. 4,703,756 an electrochemical system includes a sensor module suitable for implantation in the body to monitor glucose and oxygen levels therein. In U.S. Pat. No. 5,914,026 an implantable sensor comprising a biocompatable electroconductive case which houses a measuring electrode, a reference electrode, an auxiliary electrode, and an electronic circuit for measuring the response of the measuring electrode where the measuring electrode, reference electrode and auxiliary electrode are not in direct electrical contact with one another is provided.
This invention describes a generic implantable puck that can be used with a number of biosensor configurations. This generic implantable potentiostat telemetry unit (the puck) can also be part of a system to detect glucose concentrations. An electrochemical system partially implantable into a body for detecting glucose concentrations therein is presented. The system comprises an electrochemical sensor, a transmitting puck including an electric circuit connected to the electrochemical sensor for transmitting a signal indicative of the glucose concentrations in the body. There is at least one receiver for receiving the signal from the transmitting puck and a computer system coupled to the at least one receiver for processing the signal for patient diagnosis and treatment.